"They want to make it harder for manufacturers to sell Android devices," Google Chief Legal Officer David Drummond wrote on a company website. "Android's success has yielded something else: a hostile, organized campaign against Android by Microsoft, Oracle, Apple and other companies, waged through bogus patents," he added.

Microsoft's officer claims that Oracle, Microsoft and Apple are banding together to acquire Novell's old patents (the "CPTN" group including Microsoft and Apple) and Nortel's old patents (the "Rockstar" group including Microsoft and Apple), to make sure Google didn't get them; seeking $15 licensing fees for every Android device; attempting to make it more expensive for phone manufacturers to license Android than Windows Phone 7; and even suing Barnes & Noble, HTC, Motorola, and Samsung.

"Patents were meant to encourage innovation, but lately they are being used as a weapon to stop it," Drummond added.

"This strategy is also escalating the cost of patents way beyond what they're really worth. The winning $4.5 billion for Nortel's patent portfolio was nearly five times larger than the pre-auction estimate of $1 billion. Fortunately, the law frowns on the accumulation of dubious patents for anti-competitive means - which means these deals are likely to draw regulatory scrutiny, and this patent bubble will pop," he said.

Google is determined to preserve Android as a competitive choice for consumers, "by stopping those who are trying to strangle it."

Google is trying to buy patents to beef up its patent portfolio. Its rivals outbid the company last month in the biggest patent auction in history, $4.5 billion for more than 6,000 patents and applications for wireless technologies purchased from the bankrupt Nortel. The Department of Justice has forced the group to license the former Novell patents on fair terms, and it's looking into whether Microsoft and Apple acquired the Nortel patents for anti-competitive means.

Google this week hired away one of the Federal Trade Commission's top patent lawyers. It also bought more than 1,000 patents from IBM Corp. to defend itself from an onslaught of patent-infringement litigation.

Oracle sued Google last year in federal court, claiming its Android mobile device software infringes Oracle's Java patents, which it picked up in 2010 when it bought Sun Microsystems Inc. Oracle is seeking billions of dollars in damages. The case is set for trial in October.

"We're also looking at other ways to reduce the anti-competitive threats against Android by strengthening our own patent portfolio. Unless we act, consumers could face rising costs for Android devices - and fewer choices for their next phone," Drummond added.